1. Field of Invention
This invention is directed to a printer architecture in which the printhead carriage assembly is attachably supported to an endless drive belt so as to be driven around a radius of the belt, preferably in endless loop fashion.
2. Description of Related Art
In known printing and typing machines, a printhead is traversed across a recording medium, such as paper, in a reciprocating (back-and-forth) fashion by means of a carriage transport apparatus consisting of drive belts, lead screws, wires and/or other devices. The printhead may then further be constrained for linear movement along a printing axis by various support devices, such as tracks, sliders and carriage guide rods. For processing reasons, current architectures scan a printhead across a print zone at a constant speed. However, once the edge of the print zone is reached, the printhead must be stopped and accelerated in an opposite direction back to the constant speed prior to the print zone to continue printing. As such, these printing architectures require a non-print slow down zone at each lateral end of the printer.
A typical conventional printer with such a reciprocating carriage assembly is illustrated in FIG. 1 in which a printer, such as illustrated ink jet printer 100, includes an ink jet printhead cartridge 110 mounted on carriage 120 supported by carriage rails 130. The printhead cartridge 110 contains a housing containing ink and expels the ink through various ejector nozzles 112 under control of electrical signals received from a controller/CPU 140.
When printing, the carriage 120 reciprocates back and forth along carriage rails 130 in the direction of arrow FS. This movement is achieved by a reciprocating drive assembly 150. Reciprocating drive assembly 150 typically consists of an endless belt 152 rotatably mounted on a drive roller 154 and an idler roller 156. Drive roller 154 is driven by a reversible motor 158, such as a servo motor, under control of controller/CPU 140. Since printhead carriage 120 is fixed to the endless belt 152, carriage 120 housing printhead cartridge 110 follows the reciprocating path of endless belt 152 while being linearly guided by carriage rails 130. Proper positioning of the printhead and carriage is maintained by a conventional encoder system, such as a linear encoder consisting of an optical sensor 160 and a linear encoder fence or strip 162 mounted in scan direction FS. As the carriage is moved, the sensor 160 senses the passages of evenly spaced, alternating light and dark areas on the strip, which are used to compute travel distance and relative location as is known.
As the printhead cartridge 110 is traversed back and forth across the print zone, droplets of ink are expelled from select nozzles 112. During each pass, substrate P is maintained fixed. This provides a band or swath of print of a height H corresponding to the height of the printhead nozzle array. For purposes of print control, the reciprocation motion through a print zone laterally defined by substrate P is at a constant speed.
At the end of each pass or upon completion of multiple passes when in a multiple pass mode, the substrate P is advanced in a paper advance direction substantially perpendicular to the scanning direction FS.
There are many practical limits to the printing speed of such a conventional print engine architecture. Even as the firing frequency and number of nozzles in an ink jet printer have increased, carriage motion and paper handling have become major limiting factors in printer throughput. Reciprocating printing by back and forth movement of the print carriage at higher speeds has diminishing returns in throughput because increased carriage velocity requires increased travel distances at the ends of the reciprocating path to slow, stop, and reaccelerate the carriage to a desired constant printing speed. That is, this conventional architecture requires additional travel lengths L on both ends of the print zone in order to accelerate the carriage from a stop position to the desired constant speed before the beginning of the print zone, and to allow a deceleration zone at the end of the print zone in which to slow the carriage to a full stop, reverse direction, and reaccelerate the carriage to the desired constant speed before the carriage reaches the print zone in a reverse pass.
As the constant print speed increases, this extra travel distance L must be increased to fully slow or accelerate the carriage from higher speed, or requires substantially higher g-forces and loads on the carriage, drive motors and other printer components to achieve increased acceleration/deceleration rates. However, because there are practical limits to the g-forces sustainable by such components, typically around 1–2 g, the extra print speed typically equates to a longer travel path L. The longer travel path L makes the width of the printer housing longer, i.e., increases its footprint, and requires additional non-print time to achieve the reciprocal movement. Moreover, higher terminal velocities and acceleration/deceleration rates have adverse effects on the reliability and accuracy of carriage components.
For example, assume that a conventional printer for printing an 8″×10″ print zone (roughly the printable size on a standard 8.5″×11″ paper) uses a 1″ printhead array (i.e., prints with a 1″ print swath) to print at a constant scan speed of 45 inches/second (ips) with a typical 1 g acceleration/deceleration profile at the beginning/end of each pass. To print a full sheet of paper would require 10 passes in single pass mode.
This conventional architecture requires the moving printhead carriage to stop and reverse its direction. Assuming a constant acceleration of v=v0+a(t), stopping from 45 ips and returning to 45 ips in the opposite direction equates to45 ips=−45 ips+(1 g=9.81 m/s2)(t).
Solving this results in a total time t=0.233 seconds for the complete deceleration/acceleration cycle in the non-print zone.
The standard configuration for print zone overtravel iss=s0+v0t+0.5 at2.
Solving this for the above example is s=0+45 ips (0.1165 sec)+0.5(9.81 m/s2)(0.1165)2=2.62 inches. Therefore, in this exemplary conventional architecture, a theoretical non-printing zone of a length L of at least 2.62 inches is necessary at each end of the travel path to accommodate the deceleration/acceleration.
Prior attempts to further increase throughput have focused on increased carriage/printhead size. For example, it is known to provide full paper width printhead arrays that do not reciprocate. Rather, a recording medium is linearly advanced past the fullwidth array to print at high throughput. However, fullwidth arrays are expensive. Bigger printhead size also has its limitations. Although this allows more effective printing area coverage per swath, the extra weight and size are counterproductive to increased printing carriage motion, since the added weight affects the forces acting on the carriage. As such, there are practical limitations to the speed at which such an increased printhead can be reciprocated. Moreover, as mentioned above, minor increases in printing speed across the print zone may be offset by necessitated increased non-print time in the non-print zones.